1. Field of the Invention
The present invention relates to a land grid array (LGA) connector for electrically connecting a CPU to a printed circuit board, especially an LGA connector combined with land grid array and ball grid array techniques and having a strain relief structure preventing solder balls from being damaged by an urging force which is required in the LGA technique.
2. The Prior Art
Land grid array (LGA) connectors are commonly used with IC packages and do not require soldering procedures during engagement between the LGA connector and a related printed circuit board (PCB). Normally, an LGA assembly includes an IC package having a plurality of flat contact pads formed on a bottom surface thereof, a connector having an insulative housing and defining a plurality of passageways therethrough, and a plurality of conductive contacts received in the passageways of the connector. Fastening means comprises a top plate positioned on a top surface of the IC package, a bottom plate positioned on a bottom surface of the PCB, and a plurality of sets of aligned holes defined through the PCB. The fastening means is used to configure the assembly. Each set of aligned holes receives a screw therein which engages with a washer and a nut thereby sandwiching the LGA assembly between the top and bottom plates of the fastening means.
U.S. Pat. No. 5,653,598 discloses an electrical contact for use in a connector 30 between mutually opposed electrical interfaces 40, 99 such as contact pads respectively formed on an IC package 2 and a printed circuit board 9, as shown in FIG. 8. The conventional contact comprises a generally planar contact body 10 having first and second major faces 110, 120. The body includes a pair of spaced apart spring arms 140, 150 connected by a resilient bight portion 160. The spring arms 140, 150 each have a free end with an outwardly facing edge forming a contact nose 17, 18 for engaging with the corresponding interface 40, 99. Shorting sections 19, 20 generally extend toward each other from the free ends and are offset such that, upon deflection of the spring arms 140, 150 toward each other, the shorting sections 19, 20 overlap and the first major face 110 engages the second major face 120. Thus, a shortened electrical path is formed between the contact noses 17, 18 when the package 2 is urged against the connector 30.
The shorting sections 19, 20 may not properly contact each other due to unwanted lateral deflection thereof when the bight of the contact is deformed. Although the inner wall of the passageway receiving the contact may be used to limit the lateral deflection of the shorting sections 19, 20, unwanted scraping of the shorting sections 19, 20 against the inner wall of the passageway may occur thereby adversely affecting the proper overlap of the two shorting sections 19, 20. Proper overlap and engagement of the two shorting sections 19, 20 is difficult to achieve with this structure. Moreover, an additional contact resistance exists between the shorting sections 19, 20 thereby adversely affecting the signal transmission.
Additionally, the conventional LGA connector is in advance fixed in a motherboard via screws in a pre-assembly procedure. In a final assembly procedure, the screws have to be released first and then fastened for urging the CPU to the LGA connector. Therefore, in the total assembly procedure, the screws have to be fastened, released, and fastened again. This is cumbersome and not accepted by most mother board manufacturers.
U.S. patent application Ser. No. 09/434,593 invented by Bob McHugh, Nick Lin, Hanchen Tan, and Jwomin Wang, filed on Nov. 5, 1999 (Serial number unknown) which belongs to the same assignee with the present application, has disclosed a connector having a combined LGA/BGA structure for solving the above problems of the prior art. Such a connector comprises an insulative housing having a plurality of passageways for receiving corresponding number of contacts therein. Each contact has a contacting section for contacting with a corresponding contact pad of a CPU package which urges the connector, a surface mount section for mounting a solder ball thereon thereby connecting to a printed circuit board via the solder ball, and a resilient neck connected between the contacting section and the surface mount section for providing a tension forcing the contacting section to electrically abut against the CPU package when the contacting section is urged by the CPU package. Although this structure works well in solving the problems of the prior art, it may encounter a problem of damaging the connection of solder ball to either the connector or the printed circuit board due to the urging of the CPU package to the connector. Specifically, the solder ball is in advance soldered on the surface mount section of the contact and then experiences a reflow procedure in order to further connect to the printed circuit board. The solder ball may be forced to disconnect from either the connector or the printed circuit board thus causing malfunction when the CPU package urges the connector. It is requisite to provide a new structure to solve the problem.